Silencing Threonine Deaminase and JAR4 in Nicotiana attenuata Impairs Jasmonic Acid-Isoleucine-Mediated Defenses against Manduca sexta

• Published in: The Plant cell 2006-11, Vol.18 (11), p.3303-3320
• Main Authors: Kang, Jin-Ho, Wang, Lei, Giri, Ashok, Baldwin, Ian T
• Format: Article
• Language: English
• Subjects: Amino acids; Animals; Biosynthesis; Butyrates - metabolism; Cyclopentanes - metabolism; Cyclopentanes - pharmacology; Frass; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Plant - drug effects; Gene Silencing; Herbivores; Immunity, Innate - drug effects; Immunity, Innate - immunology; Insect larvae; Isoleucine - metabolism; Isoleucine - pharmacology; Larvae; Leaves; Manduca - physiology; Manduca sexta; Molecular Sequence Data; Nicotiana - enzymology; Nicotiana - growth & development; Nicotiana - metabolism; Nicotiana - parasitology; Nicotiana attenuata; Nicotine - metabolism; Oxylipins; Plant Diseases - immunology; Plant growth; Plant Leaves - drug effects; Plant Leaves - enzymology; Plant Leaves - parasitology; Plant Viruses - physiology; Plants; Proteinase inhibitors; RNA, Messenger - genetics; RNA, Messenger - metabolism; Signal Transduction - drug effects; Suppression, Genetic - drug effects; Threonine - metabolism; Threonine Dehydratase - genetics; Threonine Dehydratase - metabolism; Transcriptional regulatory elements; Transgenic plants; Trypsin Inhibitors
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.106.041103

Threonine deaminase (TD) catalyzes the conversion of Thr to α-keto butyrate in Ile biosynthesis; however, its dramatic upregulation in leaves after herbivore attack suggests a role in defense. In Nicotiana attenuata, strongly silenced TD transgenic plants were stunted, whereas mildly silenced TD transgenic plants had normal growth but were highly susceptible to Manduca sexta attack. The herbivore susceptibility was associated with the reduced levels of jasmonic acid-isoleucine (JA-Ile), trypsin proteinase inhibitors, and nicotine. Adding [¹³C₄]Thr to wounds treated with oral secretions revealed that TD supplies Ile for JA-Ile synthesis. Applying Ile or JA-Ile to the wounds of TD-silenced plants restored herbivore resistance. Silencing JASMONATE-RESISTANT4 (JAR4), the N. attenuata homolog of the JA-Ile-conjugating enzyme JAR1, by virus-induced gene silencing confirmed that JA-Ile plays important roles in activating plant defenses. TD may also function in the insect gut as an antinutritive defense protein, decreasing the availability of Thr, because continuous supplementation of TD-silenced plants with large amounts (2 mmol) of Thr, but not Ile, increased M. sexta growth. However, the fact that the herbivore resistance of both TD- and JAR-silenced plants was completely restored by signal quantities (0.6 μmol) of JA-Ile treatment suggests that TD's defensive role can be attributed more to signaling than to antinutritive defense.